Mg-mn-al ferrite body for microwave application

ABSTRACT

A FERRITE BODY USEFUL IN MAKING E.G. MICROWAVE CIRCUIT ELEMENTS AND HAVING NARROW $H CHARACTERISTICS, RELATIVELY HIGH CURIE TEMPERATURE, LOW SATURATION MAGNETIZATION, SMALL COERCIVE FORCE AND GOOD SQUARENESS RATIO IS CONSTITUTED BY A MG-MN-AL FERRITE COMPOSITION WITH A POROSITY LESS THAN 2% AND AN AVERAGE GRAIN SIZE OF 0.5 TO 20U OR 100 TO 500U. OPTIMAL COMPOSITIONS COMPRISE MGO 45 TO 50 MOL PERCENT, FE2O3 35 TO 45 MOL PERCENT, AL2O3 5 TO 15 MOL PERCENT AND MNO 0.1 TO 7.0 MOL PERCENT. IMPROVED $H IS ACHIEVED BY THE ADDITIONAL PRESENCE OF 0.1 TO 5 WT. PERCENT OF Y2O3, ZRO2 OR BI2O3 OR 0.1 TO 5 WT. PERCENT OF ADDITIONAL MGO. A &#34;SITE RATIO&#34; OF MG IONS FROM 0.5 TO 0.2 IS DESIRABLE.

Feb. 16,1971

Mg-Mn YUTAKA NEICHI ETAL A1 FERRITE BODY FOR MICROWAVE APPLICATION Filed Aug. 22, 1967 United States Patent Japan Filed Aug. 22, 1967, Ser. No. 662,520 Int. Cl. C04b 35/26 US. Cl. 252-6258 2 Claims ABSTRACT OF THE DISCLOSURE A ferrite body useful in making e.g. microwave circuit elements and having narrow AH characteristics, relatively high Curie temperature, low saturation magnetization, small coercive force and good squareness ratio is constituted by a Mg-Mn-Al ferrite composition with a porosity less than 2% and an average grain size of 0.5 to 20p or 100 to 50011.. Optimal compositions comprise MgO 45 to 50 mol percent, Fe O' 35 to 45 mol percent, A1 0 5 to 15 mol percent and MnO 0.1 to 7.0 11101 percent. Improved AH is achieved by the additional presence of 0.1 to 5 wt. percent of Y O ZrO or Bi O or 0.1 to 5 wt. percent of additional MgO'. A site ratio of Mg ions from 0.5 to 0.2 is desirable.

This invention relates to a microwave circuit element and more particularly to ferrite bodies adapted for microwave applications, and especially to ferrite compositions consisting of Mg-Mn-Al ferrities, and also to a method for making such ferrite bodies.

Recent electronic engineering has required a ferrite composition suitable for use in microwave applications such as in circulators, insulators and gyrators. Particularly a development in a non-reciprocal circuit in the VHF. or U.H.F. region requires a special ferrite with high resistivity, low saturation magnetization value, and high Curie temperature. Such applications require especially a ferrite body having a narrow ferromagnetic resonance line width AH, a small coercive force and a good squareness ratio in the hysteresis loop.

Accordingly, it is a principal object of this invention to provide a sintered polycrystalline ferrite body having a narrow AH characteristics for use in a non-reciprocal circuit in the U.H.F. or V.H.F. region.

Another object of the invention is to provide a squareloop ferrite composition with a relatively high Curie tem perature, a low value of saturation magnetization and a small coercive force.

A further object of the invention is to provide a method for making a ferrite body having narrow AH characteristics accompanied with a relatively high Curie temperature, a low saturation magnetization, a small coercive force and a good squareness ratio.

These and other objects of the invention will be apparent upon consideration of the following detailed description taken together with the accompanying drawings wherein:

FIG. 1 is a perspective view of an illustrative circulator comprising two ferrite bodies and a strip conductor;

3,563,898 Patented Feb. 16, 1971 "ice FIG. 2 is a graph illustrating the line width versus the porosity of said sintered ferrite;

FIG. 3 is a graph illustrating the line width versus the average grain size of said ferrite in accordance with the invention.

Before proceeding with the detailed description of the microwave circuit element contemplated by the invention, an example of the construction thereof will be described with reference to FIG. 1 of the drawing wherein reference character 10 designates, as a whole, a microwave circuit element having, as active component, preferably disc-shaped bodies 1 of ferrite body according to the present invention.

Said bodies 1 are attached together through strip conductor 2 and are magnetized with an external magnetic field perpendicular to the surface of said ferrite bodies 1.

The ferromagnetic resonance line width AH is defined as the distance AH on the field scale at a constant frequency between the sides of the ferromagnetic resonance absorption curve at mid-height, as expressed in the literature, for example, Ferromagnetic Resonance, chap. I, Sec. 10, p. 66, edited by S. V. Vonsovskii, Pergamon Press, 1966. The line width AH is measured by a cavity resonator method at a frequency of about 9600 mc.

According to the present invention a Mg-Mn-Al ferrite body provided with a porosity less than 2% and an average grain size less than 30p or higher than p. produces a narrow ferromagnetic resonance line width, AH.

A superior AH can be achieved by employing a Mg-Mn-Al ferrite body having a porosity less than 2% and an average grain size of 0.5 to 20 or 100 to 500p. in accordance with this invention.

Moreover, according to the present invention the AH of said Mg-Mn-Al ferrite having a porosity less than 2% and an average grain size less than 30 1. or higher than 100;]. can be further lowered by air-quenching the sintered body from a temperature higher than 1200" C.

The average grain size is determined by calculating the number of grains in a given area of a microscopic photograph in a given magnification in association with a method defined at pages 1690 to 1693 of the 1955 Book of ASTM, i.e. E89-52. The porosity of the ferrite is defined by the following formula:

where D is X-ray density and D is bulk density.

A Mg-Mn-Al ferrite is known to be of a mixed spinel structure in which Mg ions occupy partly the A- sites and partly the B-sites of the structure. The present ferrites have the following formula:

0.9; v 51.0 and Ow+2x02 The cation distribution in the ferrite is where and denote an A-site and B-site of the spinel lattice, respectively. The site ratio of Mg ions at the A-sites to those at the B-sites, namely .f/(l -E), can be controlled by a heat-treatment. That is, the ratio of a given composition is determined by a heating temperature and a cooling rate from said heating temperature to room temperature (about 15 to 30 According to the present invention the AH of ferrite depends greatly on said site ratio. An optimal site ratio of Mg ions is from 0.2 to 0.5 in accordance with the present invention.

Said site ratio of a given composition varies with the heating temperature and is frozen at room temperature by rapid quenching. A desired site ratio can be obtained by controlling the final heating temperature and the cooling rate in association with the weight of heated samples. A conventional method for obtaining a desired site ratio is to air-quench the ferrite body from the final heating temperature to room temperature. A more precise method is to reheat the furnace-cooled body having a specified porosity and average grain size at a temperature at which a desired site ratio is achieved and to air-quench individually the reheated body to room temperature. The site ratio frozen at room temperature can be determined by a saturation magnetization method disclosed by E. W. Gorter, Philips Res. Rep. 9 (1954) 295-365, 403-443, Saturation magnetization and crystal chemistry of ferromagnetic oxide.

A ferrite body having a porosity less than 2% and an average grain size less than 30p. can be prepared by employing a hot-press technique. A mixture of a desired composition is charged to a silicon-carbide die which can be supplied with a compacting pressure through punches during heating by using a pressing machine. Said die is preferably lined with a material inert to said ferrite composition. Said mixture is initially heated to a sintering temperature of 1100 C. to 1450 C. without any pressure at a heating rate of 100 C./hr. to 1000" C./hr. by any available and suitable heating method. Said mixture is maintained at said sintering temperature for 30 minutes to 6 hours while being pressed at a pressure of 50 to 5000 kg./cm. After pressing, the hot-pressed body is airquenched to room temperature of about 15 to 30 C.

A ferrite body having a porosity less than 2% and an average grain size higher than 100;; can be achieved by employing a hot-press technique which differs slightly from that suitable for making a ferrite body having a porosity less than 2% and an average grain size lower than 30y. as mentioned above. A mixture of a desired composition is charged to a refractory die which can be supplied with a compacting pressure through punches during heating by using a pressing machine. Said refactory die is made of any suitable refractory material such as silicon carbide, silicon nitride or graphite and optimally is lined with a material inert to said ferrite composition. Said mixture is initially heated to a sintering temperature of 1100 C. to 1400 0., without applying any pressure, at a heating rate of 100 C./hr. to 1000 C./hr. and is maintained at said sintering temperature for 30 minutes to 10 hours while being pressed at a pressure of 50 to 500 kg./cm. After pressing, the hot-pressed body is heated to a temperature higher by at least 50 C. then said first temperature and is maintained at that temperature for 30 to 180 minutes without pressing. Subsequently, the heated body is air-quenched to room temperature of about to 30 C.

Referring to FIG. 2, curve A iallustrates the relation of AH to the porosity of an Mg-Mn-Al ferrite body of an average grain size of 30a and furnace-cooled from 1300 C. Said Mg-Mn-Al ferrite consists of 47.5 mol percent of MgO, 2.5 mol percent of MnO, 2.0 mol percent of Mn O 7 mol percent A1 0 and 41 mol percent of Fe O It will be clear from the curve A that the AH increases with an increase in the porosity and is low at a porosity less than 2%.

Curve B in FIG. 2 illustrates the relation of the AH to the porosity of an Mg-Mn-Al ferrite of an average grain size of 30 and air-quenched from 1300 C. The composition of the Mg-Mn-Al ferrite is the same as that of the ferrite body of the curve A. It will be clear from the curve B that the air-quenching process remarkably improves the AH.

Curve C of FIG. 2 illustrates the relation of the AH to the porosity of an Mg-Mn-Al ferrite body of an average grain size less than 10g and air-quenched from a temperature of 1300 C. The composition of said Mg-Mn-Al ferrite is the same as those of the ferrite bodies of the curves A and B. It is readily understood that the AH can be further lowered by making an average grain size less than 10, in addition to air-quenching and by making the porosity less than 2%.

The effect of the average grain size on the AH of an Mg-Mn-Al ferrite having a porosity of about 2% is shown more clearly by the curve of FIG. 3. Said ferrite body consists of the same composition as that of the Mg-Mn-Al ferrite body of FIG. 2 and is airquenched from a temperature of 1300" C. The AH increases with an increase in the average grain size up to about and decreases with an increase in the average size as shown in FIG. 3. It will be clear that a low AH can be obtained with an Mg-Mn-Al ferrite body having an average grain size excluding a value of about 30 to 10011..

The optimal base composition of said Mg-Mn-Al ferrite is listed in Table I:

TABLE I Preferable Optimal mol mol percent percent EXAMPLE 1 A mixture consisting of the following composition of Table 2.

TABLE 2 M01 percent F6203 41 A1 0 7 MgO 47.5 M1102 4.5

is calcined at a temperature ranging between 800 C. and 1200 C. for 3 hours in air and cold-pressed into a disc form. The pressed disc body is fired at a temperature of 1350 to 1400 C. for a time period of 2 to 20 hours in air and is furnace-cooled or air-quenched to room temperature of 15 to 30 C. The cooled disc is then lapped at the surfaces into a form 0.1 mm. thick and 1.5 mm. diameter. The resultant disc is examined with respect to average grain size, porosity, the site ratio of Mg ions and the AH, the results being indicated in Table 3.

TABLE 3 Firing Sintered Average Calcined Temp, Periods, Cooling grain Porosity, Site H, temp., 0. hours size, [L percent ratio 0e.

Sample No.

1. 1,200 1,350 Furnace-cooled 15 4.1 0.2 160 2. 1,000 1,350 5 do 15 3.0 0.2 135 s. 900 1,400 do 30 2. 0 0.2 115 4 800 1,400 do 30 1.2 0.2 110 5- 1,200 1,350 2 Air-quenched---" 10 5.0 0.42 200 5 1,200 1, 350 5 d0 15 3.8 0.42 155 7... 1, 000 1, 350 15 3. 0 0. 42 125 s 1, 000 1', 400 2. 5 0. 44 100 9 900 1, 400 2. 0 0. 44 85 10.. 300 1, 400 1. 2 0. 44 70 11 800 1, 30 1. 0 0. 44 55 EXAMPLE 2 30 grams of a calcined mixture having a composition TABLE5 of Table 2 is hot-pressed, using a SiC die provided with 2 Quenching Curie asat SiC punches. The die containing the calcined nnxture 1s emp., temp, 0 K., Site heated to a temperature of 1300 to 1450 C. without applying pressure and thenis kept at said temperature Sample No.: for a time period of 1 to 6 hours while applying a pressure 15 65 213 5 435 2 1, 300 70 221 49.5 0. 40s of to 500 kg./cm. After hot pressing, the die con- 25 1,200 75 232 39.0 0. 33s talmng the hot-pressed body 1s air-quenched to room a 33- 8- 3;

temperature of 15 to 30 C. The hot-pressed body is cut and lapped into a disc of 0.1 mm. thick and 1.5 mm. diameter. The AH of the resultant disc is measured at 9600 m.c.; the results are listed in Table 4 as a function Slte rat1o=Number of Mg ions at A site/number of Mg ions at B site.

2 Furnace=cooled.

of the grain size, porosity, and the site ratio of Mg ions. 30

TABLE 4v Hot pressing Temper- Average ature, Time, Pressure, grain Porosity, Site AH, 0 hours kgJcmfl size, [5 percent ratio 0e.

The magnetic and electrical properties of the ferrite are EXAMPLE 5 as follows: a saturation magnetization 47T'MS-1800 Th e com sitlon accordrn to Table 2 has mcor rated e.m.u./cc., Cur1e temperature Tc-210 C., a coercive p0 g p0 force for Hc 0.8 oe., a squareness ratio Br/Bm 0.8 and a resistivity p 10 ohm-cm.

EXAMPLE 3 A calcined mixture having a composition according to Table 2 is hot-pressed after the manner described in Example 2. The die containing the calcined mixture is heated up to 1350 C. Without applying pressure and then is kept at the said temperature for a time peroid of 5 hours while being pressed at a pressure of 300 kg./cm. After pressing, the hot-pressed body is heated to 1450 C. and maintained at this temperature for 2 hours without pressing, and thereafter is air-quenched to room temperature. The average grain size of the hot-pressed ferrite is 100,11 and the AH is 65 0e. Other properties are similar to those described in Example 2.

EXAMPLE 4 A mixture of the composition set forth in Table 2 is calcined at 1000 C. for 1 hours in air and then coldpressed into disc form. The pressed body is fired at 1400 C. for 20 hours in air. The fired body is air-quenched from the firing temperature of 1400 C. or is cooled gradually to various temperatures of 1300, 1200 and 1000 C. so as to be air-quenched from the various temperatures to room temperature of 15 to 30 C. Before being air-quenched, the disc is kept at various temperatures for 5 hours so as to be in an equilibrium state with respect to the site ratio of Mg ions at the respective temperatures. The AH of the resultant disc is measured after the manner of the foregoing examples, and the results are listed in Table 5 as a function of Curie temperature, saturation magnetization and the site ratio of Mg ions. The resultant disc has a porosity of about 1.2% and an average grain size of 30 regardless of the quenching temperature.

therein 0.1 to 10.0 weight percent of additive Y O ZrO or Bi O The mixture is treated after the manner described in Example 1 so as to be formed into adisc. The fired disc is air-quenched from 1400 C. The AH, Tc and 41rMS of the resultant disc is measured and listed in Table 6. The site ratio of the resultant disc is about 0.44 and does not vary with addition of various weight percents of the additive.

TABLE 6 Additive Currie temper- Weight, ature, 41rMs, Material percent AH, oe. C. e.m.u./cc.

Sample No.:

20 0.1 50 200 1, 850 21 1. 0 40 195 1, 900 22. YgOa 5. 0 55 103 2, 000 23 10. 0 105 2, 050 24 0. 1 55 200 1,850 25- 1. 0 40 200 1, 850 26- ZrOz 5. 0 50 205 1, 900 27- l0. 0 95 205 1, 900 28-- 1. 0 55 208 1, 750 28- 1. 0 60 221 1, 700 30 E1 0 5. 0 70 253 1, 600 31 10. 0 85 284 1, 600

EXAMPLE 6 The composition of Table 2 has incorporate therein the additives listed in Table 7. The mixture is treated after the manner of Example 6. The AH, Curie temperature and 41rMS of resultant disc are measured and the results are listed in Table 7.

7 SCHEDULE OF ABBREVIATIONS AND SYMBOLS Abbreviation symbol: Meaning D Bulk density. D X-ray density. p Porosity. AH Ferromagnetic resonance line width. Tc Curie temperature. Hc Coercive force. Br Residual magnetic inductance. Bm Maximum magnetic inductance. p Electrical resistivity. Saturation magnetic moment. Ms Saturation magnetization. V.H.F. Very high frequency ranging from 30 mc. to 300 mc. U.H.F. Ultra high frequency ranging from 300 mc. to 3000 mc.

E.m.u. Electro-magnetic unit. A- and B- site Cation lattice site of spinel lattice.

What is claimed is:

1. A microwave circuit element comprising a Mg-Mn-Al ferrite body having a porosity less than 2%. a site ratio of Mg ions from 0.2 to 0.5, and an average grain size ranging from 0.5 to 500 excluding to 100p, said ferrite body having a basic composition comprising to mol percent of magnesium oxide, 35 to 50 mol percent of ferric oxides, 5 to 15 mol percent of aluminum oxide and 0 to 5 mol percent of manganese oxide, wherein said basic composition additionally contains 0.1 to 5 wt. percent of at least one member selected from the group consising of Y O Zr0 and Bi O 2. A microwave circuit element according to claim 1, wherein said basic composition additionally contains 0.1 to 5 wt. percent of MgO.

References Cited UNITED STATES PATENTS 3,002,929 10/1961 Van Vitert 25262.58 3,034,986 5/1962 Baird et al 252-62.64 3,023,165 2/1962 Van Vitert 252-6258 3,189,550 6/1962 Malinofsky 25262.62

20 TOBIAS E. LEVOW, Primary Examiner R. D. EDMONDS', Assistant Examiner US. Cl. X.R. 252,62.64 

